The present invention relates to a tamper-evident closure construction for use with bottles and other containers and is particularly directed to a container having a neck, or "finish", configured to receive a twist-off cap which when once removed will provide the user with a readily observable indication that the container has previously been opened. In the past, a number of closure constructions have been proposed, including caps and arms, to seal the tops of bottles in such a manner that once the cap has been removed it provides a visual indication that the container has been opened. Such closures have been designed with the intent of preventing the practice of removing the cap to permit the introduction of a contaminant into the container and subsequently replacing the cap so that a subsequent user unknowingly ingests the contaminant.
One approach to the construction of tamper-evident closures in the past has been to provide detents or other protrusions on the bottle which deform portions of a thin metal cap when the cap is rotated during removal. This approach is exemplified in Sharp U.S. Pat. Nos. 1,796,728 and 1,796,729. A second approach is shown in Amabili U.S. Pat. No. 4,055,266. The closure construction disclosed in this patent includes a twist-off cap having one or more flanges which are turned under a bead provided on the bottle. The cap includes a series of lines of weakening, along which the flange ruptures or separates when it is removed, to provide a visual indication that the cap has been removed. These prior art closure constructions have not been totally satisfactory for various reasons. For example, the caps of the type shown in the Sharp patents can be reapplied to the bottle and can be pressed inwardly to assume a shape sufficiently close to the original cap configuration so that some users would not realize that the cap had previously been removed. Other prior art closures are not compatible with high speed capping equipment or are too complex or cumbersome.
Another type of tamper-evident closure construction is shown in my earlier U.S. Pat. No. 4,782,969 for "Twist-Off Bottle Caps" and U.S. Pat. No. 5,263,600 for "Tamper-Evident Twist-Off Closure". The cap shown in U.S. Pat. No. 4,782,969 includes a flat top and ribbed skirt which carries along its lower edge a plurality of narrow tabs. When the cap is applied to the bottle, these tabs are bent upwardly and inwardly to engage surfaces formed on the neck of the container below an endwise lip. When the cap is in the sealed and locked position, the upwardly bent portions of the tabs are in compression and hold the cap tightly sealed against the end of the lip. The cap is removed by an initial twisting motion followed by a lifting motion. The bottle includes a plurality of ribs which cam the tabs outwardly as the cap is twisted. When the cap is lifted, the tabs are bent further outwardly by an upwardly and outwardly sloping surface of a lip on the bottle, the bending continues until the tabs are in a position to clear the lip of the bottle permitting the cap to be lifted free from the bottle. While this construction provides an effective tamper-proof seal, it is subject to the disadvantage that it requires a relatively high amount of torque to twist off the cap.
The cap shown in my U.S. Pat. No. 5,263,600 utilizes a cap including a flat top which extend from the center edge of the skirt are bent upwardly and inwardly to a depending ribbed skirt and a plurality of narrow tabs. The tabs engage a shelf formed on the bottle and hold the cap in position by compression in generally the same manner as in U.S. Pat. No. 4,782,969. The bottle further comprises a plurality of cams which cam the tabs outwardly to a position beyond the outer edge of the shelf. The free ends of the tabs in this position are not bent completely against the skirt or the cap but rather remain at a slight angle. The lip extends upwardly and outwardly from the shelf. As a result, the free ends of the tabs engage the lip so that the tabs are not free to be moved upwardly. Rather when the cap is lifted and twisted, the tabs must be cammed outwardly by the outwardly sloping surface on the bottle lip before the cap can be pulled completely free of the bottle. The tabs disclosed in this patent are of an asymmetrical configuration with a portion adjacent one edge of the tab being slightly longer than the other to reduce the amount of torque required to twist the cap. The cap shown in my patent, U.S. Pat. No. 5,263,600 like that shown in my earlier patent, U.S. Pat. No. 4,782.969 cannot be reapplied to the bottle in their original configuration without the use of some highly sophisticated and complicated mechanism. Despite its advantages, the closure construction shown in U.S. Pat. No. 5,263,600 does present a number of disadvantages in use which are overcome by the present invention.